For example, in processes of manufacturing semiconductor devices, liquid crystal panels or the like, various processes such as deposition processes, etching processes and oxidizing processes on objects to be processed such as semiconductor substrates or substrates for liquid crystals (hereinafter, the semiconductor substrates or the substrates for liquid crystals are simply referred to as wafers W) are performed in separate processing chambers. When the objects to be processed are transferred between the processing chambers, a transfer device having a holding part for holding the objects to be processed has been normally used. There are various types of transfer devices, where a transfer device for reciprocating the holding part by extending or contracting a multi-articulated arm has been widely used, for example.
For example, a transfer device having a multi-articulated arm has been disclosed in the related art. The transfer device has two links and two arms, which are combined in a rhombus shape, where a holding part for holding an object to be processed is rotatably connected to ends of the two links, and a driving mechanism such as a motor is connected to ends of the two arms. As the two links connected to the driving mechanism are rotated in opposite directions, the holding part may be operated to be extended and contracted.
In this transfer device, the object to be processed is required to be transferred with high accuracy to a desired position within a processing chamber. However, only the rotatable connection of the holding part to the ends of the two links cannot consistently maintain a rotational position of the holding part, so that it is difficult to transfer the object to be processed with high accuracy. Accordingly, as a posture holding device for holding a posture of the holing part in a desired state in this transfer device, there has been suggested a posture holding device in which the ends of additional posture-holding links are rotatably connected to the two links on the side of the holding part, respectively, while the opposite ends of the additional posture-holding links are connected respectively to a pair of rollers arranged in a vertical direction, and the rollers are inserted into a pair of rails.
Further, in order to hold the posture of the holding part, it has been known in the related art that gears are installed at respective leading ends of the two links rotatably connected to the holding part, respectively. These two gears are caused to be engaged with each other so as to synchronize the two links, thereby holding the posture of the holding part connected to the links.
However, in the transfer device described above, there may be a case in which control problem or mechanical problem causes the holding part to deviate from a predetermined route, thereby resulting in a trouble in that the holding part comes into contact with a wall surface of the processing chamber, for example. In this case, a moment is applied to the holding part in contact with the wall surface of the processing chamber, for example. However, the moment applied to the holding part cannot be avoided since the transfer device is equipped with the posture holding device for holding the posture of the holding part as described above. As a result, excessive torque may be exerted to the holding part or the posture holding device, leading to concern for breakage of the transfer device.